Solid-state imaging device and method of operating the same, and electronic apparatus and method of operating the same

ABSTRACT

A solid-state imaging device includes a plurality of pixels in a two-dimensional array. Each pixel includes a photoelectric conversion element that converts incident light into electric charge, and a charge holding element that receives the electric charge from the photoelectric conversion element, and transfers the electric charge to a corresponding floating diffusion. The charge holding element further includes a plurality of electrodes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Priority PatentApplication JP 2013-197874 filed Sep. 25, 2013, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a solid-state imaging device and amethod of operating the same, and an electronic apparatus and a methodof operating the same, and more particularly, to a solid-state imagingdevice and a method of operating the same, and an electronic apparatusand a method of operating the same which are capable of holding chargegenerated by light reception of a photodiode in a holding unit which isconstituted by a plurality of electrodes and capable of reliablytransmitting the held charge by partially generating a strong electricfield by control of turning-on or turning-off for each electrode.

A rolling shutter type device that sequentially reads out photoelectricconversion electrons for each pixel is generally used as a complementarymetal oxide semiconductor (CMOS) type image sensor.

However, in the rolling shutter type device, since there is no temporalsimultaneity between timings when imaging is performed in pixelsconstituting an image, an image obtained by capturing a subjectoperating at a high speed may be distorted. For this reason, a globalshutter (GS) type device has been suggested which simultaneouslytransmits photoelectrically-converted charge to another holding unit tohold the charge and then sequentially reads out the charge from theholding unit (MEM) (see Japanese Unexamined Patent ApplicationPublication No. 2008-103647).

SUMMARY

Incidentally, in the structure disclosed in Japanese Unexamined PatentApplication Publication No. 2008-103647, an attempt to form a holdingunit (charge holding unit) which holds large-capacity charge results inan increase in the size thereof.

In such a structure, when there is an attempt to transmit chargegenerated by a light receiving element to a floating diffusion, animpurity profile is generally formed so as to be capable of forming asufficient electric field between a near-field region and a far-fieldregion of the floating diffusion in the holding unit.

However, when a transmission distance is increased in a situation wherea predetermined sufficient electric field is maintained, so-called resetvoltages for depleting the holding unit increase, which results in anincrease in power consumption.

The present disclosure is contrived in view of such a situation, andparticularly, it is desirable to reliably transmit charge held in aholding unit to a floating diffusion without unnecessarily increasing areset voltage generated in association with an increase in the size ofthe holding unit.

An imaging device according to a first illustrative example of thepresent disclosure may include a plurality of pixels in atwo-dimensional array, each including: a photoelectric conversionelement that converts incident light into an electric charge; and acharge holding element that receives the electric charge from thephotoelectric conversion element, and transfers the electric charge to acorresponding floating diffusion. For each of the plurality of pixels,the charge holding element may include a plurality of electrodes.

The imaging device of the first illustrative example may further includea control circuit that controls operations of the plurality of pixels.The control circuit may be configured to cause the charge holdingelement of a given pixel of the plurality of pixels to transfer theelectric charge held therein to the corresponding floating diffusion bysequentially supplying an OFF potential to the plurality of electrodesof the given pixel.

The control circuit may be configured to drive the plurality of pixelsto perform a global shutter imaging operation.

In the imaging device of the first illustrative example, the pluralityof pixels may be grouped into units each comprising j pixels, j being aninteger greater than 1, where each of the pixels that is included in asame unit corresponds to a same floating diffusion.

The control circuit may be configured to cause a given unit to performan additive readout operation that may include transferring the electriccharges held in the respective charge holding elements of each of thepixels of the given unit to the corresponding floating diffusion suchthat the corresponding floating diffusion adds together the electriccharges transferred from the pixels of the given unit.

The control circuit may be configured to cause a given unit to perform apartial additive readout operation, which may include: for each of thepixels of the given unit, turning on less than all of the plurality ofelectrodes of the charge holding element of the respective pixel whilethe charge holding element of the respective pixel receives the electriccharge from the photoelectric conversion element of the respectivepixel, and transferring the electric charges held in the respectivecharge holding elements of each of the pixels of the given unit to thecorresponding floating diffusion such that the corresponding floatingdiffusion adds together the electric charges transferred from the pixelsof the given unit.

The control circuit may be configured selectively read out a given unitaccording to one of a plurality of readout modes that the controlcircuit may be configured to selectively switch between, the pluralityof readout modes including: an individual pixel readout mode in whichthe electric charge of the charge holding element of each pixel of thegiven unit is read out individually, an additive readout mode in whichthe electric charge of the charge holding element of each pixel of thegiven unit is added together by the corresponding floating diffusion andread out collectively, and a partial additive readout mode in which, foreach of the pixels of the given unit, less than all of the plurality ofelectrodes of the charge holding element of the respective pixel areturned on while the charge holding element of the respective pixelreceives the electric charge from the photoelectric conversion elementof the respective pixel and the electric charge of the charge holdingelement of each pixel of the given unit is added together by thecorresponding floating diffusion and read out collectively.

The control circuit may be configured to cause a given pixel of theplurality of pixels to perform a partial readout operation that includesturning on less than all of the plurality of electrodes of the chargeholding element of the given pixel while the charge holding element ofthe given pixel receives the electric charge from the photoelectricconversion element of the given pixel.

Each of the plurality of pixel may include a first transfer gate thatselectively electrically separates the photoelectric conversion elementof the respective pixel from the charge holding element of therespective pixel, and a second transfer gate that selectivelyelectrically separates the charge holding element of the respectivepixel from the corresponding floating diffusion.

The charge holding element may include a plurality of sub-regions eachcorresponding to one of the plurality of electrodes. The plurality ofsub-regions may be arranged in series between the first and secondtransfer gates. The plurality of sub-regions may be arranged such thateach adjoins the photoelectric conversion element of the respectivepixel with no other one of the plurality of sub-regions interveningtherebetween.

The plurality of sub-regions may be arranged such that a first directionis transverse to a second direction, the first direction is a directionin which charge is transferred into the charge holding element throughthe first transfer gate, and the second direction is a direction inwhich charge is transferred out from the charge holding element throughthe second transfer gate.

The charge holding element may include a plurality of sub-regions eachcorresponding to one of the plurality of electrodes, the plurality ofsub-regions may be arranged such that a first direction is transverse toa second direction, the first direction is a direction in which chargeis transferred into the charge holding element, and the second directionis a direction in which charge is transferred out from the chargeholding element.

The charge holding element of each of the plurality of pixels may beconfigured such that at least one of the plurality of electrodes thereofalso controls transfer of the electric charge from the photoelectricconversion element of the respective pixel to the charge holding elementof the respective pixel.

For a given pixel of the plurality of pixels, at least one of theplurality of electrodes of the charge holding element thereof may be adifferent size from at least one other of the plurality of electrodes ofthe charge holding element thereof.

Each of the plurality of pixels may further include aphotoelectric-conversion-element-reset gate that abuts the photoelectricconversion element and selectively connects the photoelectric conversionelement to a reset drain.

Each of the plurality of pixels may further include a light shieldingunit configured to shield the charge holding element from the incidentlight, and an electrode of at least one of the holding units may bedirectly electrically connected to the light shielding unit.

According to a second illustrative example of the present disclosure, amethod of driving an imaging device that includes a plurality of pixelsthat each include a photoelectric conversion element that convertsincident light into an electric charge and a charge holding element thatreceives the electric charge from the photoelectric conversion element,temporarily holds the electric charge, and transfers the electric chargeto a corresponding floating diffusion, where for each of the pluralityof pixels, the charge holding element includes a plurality ofelectrodes, may include: causing the charge holding element of a givenpixel of the plurality of pixels to transfer the electric charge heldtherein to the corresponding floating diffusion by sequentially turningoff the plurality of electrodes of the charge holding element of thegiven pixel.

The method may further include turning on less than all of the pluralityof electrodes of the given pixel while the electric charge is receivedfrom the photoelectric conversion element by the charge holding element.

According to a third illustrative example of the present disclosure, anelectronic apparatus may include an imaging device that includes aplurality of pixels in a two-dimensional array. The plurality of pixelsmay each include: a photoelectric conversion element that convertsincident light into an electric charge; and a charge holding elementthat receives the electric charge from the photoelectric conversionelement, and transfers the electric charge to a corresponding floatingdiffusion. The charge holding element may include a plurality ofelectrodes.

A solid-state imaging device according to an embodiment of the presentdisclosure includes a photodiode that receives light in pixel units andgenerates charge by photoelectric conversion, and a holding unit thatincludes electrodes divided into a plurality of pieces and temporarilyholds the charge generated by the photodiode. The holding unitsequentially switches turning-on or turning-off of the dividedelectrodes to thereby transmit the held charge to a floating diffusion.

The solid-state imaging device may be a global shutter type solid-stateimaging device.

The solid-state imaging device may further include an addition unit thatadds the charge transmitted from the holding units of the plurality ofpixels. Charge accumulated in a portion of the electrodes divided into aplurality of pieces may be transmitted to the floating diffusion. Theaddition unit may add the charge accumulated in the portion of theelectrodes divided into a plurality of pieces by the plurality of pixelsand then may transmit the charge.

The solid-state imaging device may further include a read-out electrodewhich is constituted by an electrode that controls the transmission ofthe charge generated by the photodiode to the holding unit. The read-outelectrode may be configured in a direction perpendicular to a divisiondirection of the electrodes divided into a plurality of pieces, whichconstitute the holding unit.

The plurality of divided electrodes constituting the holding unit may bedivided so as to have substantially equal areas.

The plurality of divided electrodes constituting the holding unit may bedivided so as to have unequal areas.

The holding unit may have a function of transmitting the chargegenerated by the photodiode to itself.

The solid-state imaging device may further include a global reset gatethat controls turning-on or turning-off for directly discharging thecharge of the photodiode to a reset drain.

The holding unit may include SiO₂, SiN, HfO₂, or TaO₂ and may be formedby a stack thereof.

A material of the electrode may be a metal material including Poly Si,PDAS, W, Mo, Al, or Cu.

The holding unit may further include a light-shielding unit, and any oneof the electrodes divided into a plurality of pieces may be shorted tothe light-shielding unit.

A method of operating a solid-state imaging device according to anotherembodiment of the present disclosure includes causing a photodiode toreceive light in pixel units and to generate charge by photoelectricconversion, and causing a holding unit with electrodes divided into aplurality of pieces to temporarily hold the charge generated by thephotodiode. The holding unit sequentially switches turning-on orturning-off of the divided electrodes to thereby transmit the heldcharge to a floating diffusion.

An electronic apparatus according to still another embodiment of thepresent disclosure is an electronic apparatus having a solid-stateimaging device. The electronic apparatus includes a photodiode thatreceives light in pixel units and generates charge by photoelectricconversion, and a holding unit that includes electrodes divided into aplurality of pieces and temporarily holds the charge generated by thephotodiode. The holding unit sequentially switches turning-on orturning-off of the divided electrodes to thereby transmit the heldcharge to a floating diffusion.

The solid-state imaging device may be a global shutter type solid-stateimaging device.

The electronic apparatus may further include an addition unit that addsthe charge transmitted from the holding units of the plurality ofpixels. Charge accumulated in a portion of the electrodes divided into aplurality of pieces may be transmitted to the floating diffusion. Theaddition unit may add the charge accumulated in the portion of theelectrodes divided into a plurality of pieces by the plurality of pixelsand then may transmit the charge.

The electronic apparatus may further include a read-out electrode whichis constituted by an electrode that controls the transmission of thecharge generated by the photodiode to the holding unit. The read-outelectrode may be configured in a direction perpendicular to a divisiondirection of the electrodes divided into a plurality of pieces, whichconstitute the holding unit.

The plurality of divided electrodes constituting the holding unit may bedivided so as to have substantially equal areas.

The plurality of divided electrodes constituting the holding unit may bedivided so as to have unequal areas.

The holding unit may have a function of transmitting the chargegenerated by the photodiode to itself.

A method of operating an electronic apparatus according to still anotherembodiment of the present disclosure is a method of operating anelectronic apparatus having a solid-state imaging device. The methodincludes causing a photodiode to receive light in pixel units and togenerate charge by photoelectric conversion, and causing a holding unitwith electrodes divided into a plurality of pieces to temporarily holdthe charge generated by the photodiode. The holding unit sequentiallyswitches turning-on or turning-off of the divided electrodes to therebytransmit the held charge to a floating diffusion.

In the embodiments of the present disclosure, light is received in pixelunits, charge is generated in a photodiode by photoelectric conversion,the charge generated by the photodiode is temporarily held by a holdingunit which is provided with electrodes divided into a plurality ofpieces, and the turning-on or turning-off of the divided electrodes issequentially switched by the holding unit, thereby transmitting the heldcharge to a floating diffusion.

According to the embodiments of the present disclosure, it is possibleto reliably transmit charge held in a holding unit to an FD unit withoutunnecessarily increasing a reset voltage generated in association withan increase in the size of the holding unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration example of a generalsolid-state imaging device;

FIG. 2 is a diagram illustrating a configuration example of asolid-state imaging device according to a first embodiment to which thepresent disclosure is applied;

FIG. 3 is a diagram illustrating a circuit configuration example of thesolid-state imaging device of FIG. 2;

FIG. 4 is a flow chart illustrating a charge accumulation transmissionprocess using the solid-state imaging device of FIG. 2;

FIG. 5 is a timing chart illustrating the charge accumulationtransmission process using the solid-state imaging device of FIG. 2;

FIG. 6 is a state diagram illustrating the charge accumulationtransmission process using the solid-state imaging device of FIG. 2;

FIG. 7 is a diagram illustrating a configuration example of asolid-state imaging device according to a second embodiment to which thepresent disclosure is applied;

FIG. 8 is a diagram illustrating potential distribution of thesolid-state imaging device of FIG. 7;

FIG. 9 is a flow chart illustrating a charge accumulation transmissionprocess using the solid-state imaging device of FIG. 7;

FIG. 10 is a timing chart illustrating the charge accumulationtransmission process using the solid-state imaging device of FIG. 7;

FIG. 11 is a diagram illustrating a configuration example of asolid-state imaging device according to a third embodiment to which thepresent disclosure is applied;

FIG. 12 is a diagram illustrating a difference between transmissionpaths of charge according to layouts of a first holding unit to a fourthholding unit;

FIG. 13 is a diagram illustrating a circuit configuration example of asolid-state imaging device according to a fourth embodiment to which thepresent disclosure is applied;

FIG. 14 is a diagram illustrating a read-out pattern of a pixel signalin the solid-state imaging device of FIG. 13;

FIG. 15 is a timing chart illustrating a charge accumulationtransmission process in a case where a pixel signal is individuallyoutput for each pixel using the solid-state imaging device of FIG. 13;

FIG. 16 is a flow chart illustrating a charge accumulation transmissionprocess in a case where a pixel signal is output by addition for everyfour pixels, using the solid-state imaging device of FIG. 13;

FIG. 17 is a timing chart illustrating the charge accumulationtransmission process in a case where a pixel signal is output byaddition for every four pixels, using the solid-state imaging device ofFIG. 13;

FIG. 18 is a timing chart illustrating another charge accumulationtransmission process in a case where a pixel signal is output byaddition for every four pixels, using the solid-state imaging device ofFIG. 13;

FIG. 19 is a timing chart illustrating another charge accumulationtransmission process in a case where a pixel signal is output byaddition for every four pixels, using the solid-state imaging device ofFIG. 13;

FIG. 20 is a diagram illustrating a configuration example of asolid-state imaging device according to a fifth embodiment to which thepresent disclosure is applied;

FIG. 21 is a diagram illustrating potential distribution of thesolid-state imaging device of FIG. 20;

FIG. 22 is a flow chart illustrating a charge accumulation transmissionprocess in a case where a pixel signal is output by addition for everyfour pixels, using the solid-state imaging device of FIG. 20;

FIG. 23 is a timing chart illustrating the charge accumulationtransmission process in a case where a pixel signal is output byaddition for every four pixels, using the solid-state imaging device ofFIG. 20;

FIG. 24 is a diagram illustrating a configuration example of asolid-state imaging device according to a sixth embodiment to which thepresent disclosure is applied;

FIG. 25 is a diagram illustrating a configuration example of asolid-state imaging device according to a seventh embodiment to whichthe present disclosure is applied;

FIG. 26 is a flow chart illustrating a charge accumulation transmissionprocess using the solid-state imaging device of FIG. 25;

FIG. 27 is a timing chart illustrating the charge accumulationtransmission process using the solid-state imaging device of FIG. 25;

FIG. 28 is a diagram illustrating a configuration example of a wiring ina solid-state imaging device of the related art; and

FIG. 29 is a diagram illustrating a configuration example of a wiring inthe solid-state imaging device to which the present disclosure isapplied.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments for implementing the present disclosure(hereinafter, referred to as embodiments) will be described. Thedescription thereof is made in the following order.

1. First Embodiment (an example of a case where a holding unit isdivided into two pieces)

2. Second Embodiment (an example of a case where a holding unit isdivided into four pieces)

3. Third Embodiment (an example of a case where a photodiode is disposedin a direction perpendicular to a direction in which a first holdingunit to a fourth holding unit are divided)

4. Fourth Embodiment (an example of a case where pixel signals of fourpixels are added)

5. Fifth Embodiment (an example of a case where a global reset gate isprovided)

6. Sixth Embodiment (an example of a case where a holding unit isunequally divided)

7. Seventh Embodiment (an example of a case where a holding unit has afunction of a transmission gate)

First Embodiment Configuration Example of General Solid-State ImagingDevice

FIG. 1 is a top view showing a configuration example of a generalsolid-state imaging device in pixel units. The left side in FIG. 1 showsa configuration example of a solid-state imaging device of the relatedart, and the right side in FIG. 1 shows a configuration example of asolid-state imaging device that has become common in recent years.

The solid-state imaging device of the related art which is shown on theleft side of FIG. 1 includes a photodiode PD, a transmission gate TG, aholding unit MEM, a floating gate FG, a floating diffusion FD, a resetgate RST, a reset drain RST Drain, an amplification unit AMP, and aselection unit SEL from the lowermost portion in FIG. 1.

The photodiode PD is constituted by a light receiving element, andgenerates charge corresponding to the amount of light by photoelectricconversion when light is received.

The transmission gate TG transmits charge accumulated in the photodiodePD to the holding unit MEM by control of turning-on or turning-off.

The holding unit MEM is controlled to be turned on or turned off, andthus functions as a gate. When the holding unit is controlled to beturned on, the holding unit temporarily holds charge transmitted throughthe transmission gate TG from the photodiode PD. In addition, theholding unit MEM is constituted by electrodes having these functions,and thus holds or transmits charge by a voltage to be applied to theelectrodes.

That is, in a case where the holding unit MEM is turned on, thetransmission gate TG transmits the charge accumulated in the photodiodePD to the holding unit MEM at the same timing with respect to all pixelswhen the turning-on of a shutter is controlled. As a result, chargeserving as a pixel signal generated by the photodiode PD is held in theholding unit MEM at the same timing with respect to all pixels. A lightshielding film F is provided in the holding unit MEM so as to shield theholding unit MEM from light. Thus, it is possible to block light comingaround from the photodiode PD and to reliably hold the amount of lightwhich is the same as the amount of light received in the photodiode PD.

The floating gate FG transmits the charge held in the holding unit MEMto the floating diffusion FD by control of turning-on or turning-off.

The amplification unit AMP amplifies a voltage of power supplied throughthe selection unit SEL at a predetermined magnification in accordancewith the amount of charge transmitted to the floating diffusion FD, andthen outputs the voltage as a pixel signal.

When a pixel signal is instructed to be transmitted by a control unitwhich is not shown in the drawing, the selection unit SEL supplies powersupplied from a power source VDD to the amplification unit AMP.

The reset gate RST discharges the charge transmitted to the floatingdiffusion FD to the reset drain RST Drain by control of turning-on orturning-off.

In addition, the configuration example of the solid-state imaging devicewhich is shown on the right side of FIG. 1 has a basic configurationsimilar to that of the solid-state imaging device on the left side, andthus the description thereof will be omitted. Incidentally, thesolid-state imaging devices on the left side and the right side of FIG.1 have different configurations in a holding capacitor that holds chargeof the holding unit MEM. That is, the solid-state imaging device on theright side of FIG. 1 has an area which is physically larger than that onthe left side, and thus the amount of charge capable of being held isincreased. An increase in the size of the holding unit MEM is for thepurpose of increasing the capacity of charge transmitted from thephotodiode PD.

For example, in the solid-state imaging device on the left side of FIG.1, charge is held in the holding unit MEM by both the transmission gateTG and the floating gate FG being turned off, as in state St1 shown onthe upper right side of the left side of FIG. 1.

In this state, when the floating gate FG is turned on, the held chargeis transmitted to the floating diffusion FD due to the influence of anelectric field generated on the holding unit MEM by an impurity profileof an electrode constituting the holding unit MEM, as indicated by stateSt2. That is, the holding unit MEM is constituted by an electrode and agate oxide film which constitutes a transmission path for transmittingcharge in an electric field generated by the electrode. For example, ina case where the holding unit MEM is controlled to be turned on by theapplication of a voltage to the electrode, charge is held within thegate oxide film of the holding unit MEM when both the transmission gateTG and the floating gate FG are in an off state. At this time, anelectric field is generated in the electrode of the holding unit MEM bythe impurity profile, and thus a potential is inclined so as to be aleft downward inclination in the drawing, as indicated by the state St1of FIG. 1. For this reason, in the state St1, when the floating gate FGis turned on, the held charge is transmitted to the floating diffusionFD due to the influence of the inclination of the potential according tothe electric field generated on the holding unit MEM, as indicated bythe state St2.

In addition, each of the states St1, St2, St11, and St12 of FIG. 1 showspotential distribution in a cross-section taken along line A-A′ in thetop view of each of the right and left solid-state imaging devices ofFIG. 1.

The holding unit MEM in recent years as shown on the right side of FIG.1 is made to have large capacity by increasing the size of theelectrode, and thus it is possible to accumulate charge in the holdingunit MEM by an operation similar to that in the state St1, as indicatedby the state St11. However, as indicated by the state St12, even whenthe floating gate FG is turned on similarly to a case of the state St2,a transmission distance is made long by an increase in the physical sizeof the electrode of the holding unit MEM. Accordingly, the inclinationof the electric field on the holding unit MEM becomes gentle, and thusthe entire charge which is held may not be transmitted to the floatingdiffusion FD, which results in the generation of remaining charge. Thatis, in the solid-state imaging device on the right side of FIG. 1, evenwhen the floating gate FG is turned on, the inclination of the potentialon the holding unit MEM becomes gentle. Accordingly, the entire chargewhich is held has a tendency not to be transmitted to the floatingdiffusion FD, which may lead to the generation of remaining charge onthe holding unit MEM.

In addition, even in such a case, a configuration can also be adopted inwhich a stronger electric field is generated by adjusting the impurityprofile of the holding unit MEM. However, in this configuration, it isnecessary to set a strong reset voltage, which results in a concern ofan increase in power consumption.

In FIG. 1, the magnitude of the change in potential on the holding unitMEM in the states St2 and St12, that is, the magnitude of theinclination of the potential distribution indicates electric fieldintensity. That is, in the state St12, the inclination of the potentialon the holding unit MEM is gentler than the inclination in the stateSt2, that is, the electric field intensity is weak, and thus a statewhere the held charge has a tendency not to be transmitted to thefloating diffusion FD is shown.

Configuration Example of Solid-State Imaging Device according to FirstEmbodiment

Consequently, in the solid-state imaging device to which the presentdisclosure is applied, as shown in FIG. 2, an electrode constituting theholding unit MEM is divided into a plurality of pieces.

The right side of FIG. 2 is a top view showing a configuration exampleof a solid-state imaging device in pixel units to which the presentdisclosure is applied. In addition, the left side of FIG. 2 shows anexample of potential distribution in a cross-section taken along lineA-B on the right side of FIG. 2. In the solid-state imaging device shownon the right side of FIG. 2, components having the same functions asthose of the solid-state imaging device of FIG. 1 will be given the samereference numerals, signs and names, and the description thereof will beappropriately omitted.

That is, the solid-state imaging device of FIG. 2 is different from thesolid-state imaging device of FIG. 1 in that an electrode constituting aholding unit MEM is equally divided into a plurality of pieces toprovide a first holding unit MEM1 and a second holding unit MEM2, and inthat an overflow discharge portion OFB is provided.

The size of the holding unit is increased as a whole by providing thefirst holding unit MEM1 and the second holding unit MEM2, and the heldcharge is more reliably transmitted to a floating diffusion FD by thecontrol thereof. In addition, the overflow discharge portion OFBfunctions as a gate of a predetermined potential, and extra chargeexceeding the amount of charge capable of being accumulated in aphotodiode PD is discharged to a reset drain RST Drain in the adjacentpixel.

In addition, the left side of FIG. 2 shows a state where a transmissiongate TG, a floating gate FG, and a reset gate RST are turned off and thefirst holding unit MEM1 and the second holding unit MEM2 are turned on.That is, for example, a state is shown in which charge that wasaccumulated in the photodiode PD is held in the first holding unit MEM1and the second holding unit MEM2 after having been transmitted throughthe transmission gate TG.

Circuit Configuration of Solid-State Imaging Device of FIG. 2

Next, a circuit configuration example of the solid-state imaging deviceof FIG. 2 will be described with reference to FIG. 3.

In a circuit configuration example of a solid-state imaging device ofFIG. 3, sources and drains of the transmission gate TG, the firstholding unit MEM1, the second holding unit MEM2, the floating gate FG,and the reset gate RST are connected in series to a cathode of aphotodiode of a pixel P. In addition, a gate of an amplification unitAMP is connected between the floating gate FG and the reset gate RST. Aselection unit SEL controls the supply of power, supplied from the powersource VDD, to the amplification unit AMP by control of turning-on orturning-off.

With such a configuration, the transmission gate TG transmits the chargeaccumulated in the photodiode PD of the pixel P to the first holdingunit MEM1 and the second holding unit MEM2 for a predetermined period oftime from a timing when an operation to control a shutter, not shown inthe drawing, is made.

Further, in a state where the selection unit SEL is turned on, when thereset gate RST is turned off and the floating gate FG is turned on, theamplification unit AMP amplifies a voltage supplied from the powersource VDD in accordance with the amount of charge transmitted from theholding unit MEM2, and then outputs the voltage as a pixel signal.

With such a configuration, the turning-on or turning-off of the firstholding unit MEM1 and the second holding unit MEM2 is sequentiallyswitched and controlled, and thus it is possible to increase the amountof charge capable of being held by increasing the electrode areas of thefirst holding unit MEM1 and the second holding unit MEM2 as a whole. Inaddition, the electrode constituting each of the first holding unit MEM1and the second holding unit MEM2 is controlled so as to increase theelectric field intensity, thereby transmitting the held charge. Thus, itis possible to temporarily hold the charge accumulated in the photodiodePD and to reliably transmit the total amount of charge held to thefloating diffusion FD.

Charge Accumulation Transmission Process Using Solid-State ImagingDevice of FIG. 2

Next, a charge accumulation transmission process of the solid-stateimaging device of FIG. 2 will be described with reference to a flowchart of FIG. 4 and a timing chart of FIG. 5. In addition, FIG. 5 showsa control state at a timing of the turning-on (High) or turning-off(Low) of each of the reset gate RST, the floating gate FG, the secondholding unit MEM2, the first holding unit MEM1, the transmission gateTG, and the selection unit SEL from above. Although this configurationin which a high potential corresponds to turning-on the pixel componentand the low potential corresponds to turning off the pixel component isillustrated in FIG. 5 and throughout this disclosure for the sake ofsimplicity, it should be noted that alternative configurations arewithin the scope of this disclosure. For example, configurations inwhich the aforementioned components are turned on by a low potential andturned off by a high potential or configurations in which a mixture ofcomponents that are turned on by a high potential and components thatcomponents are turned off by a high potential are within the scope ofthis disclosure. These alternative configurations can be achieved bysubstitution of appropriate components as known in the art (e.g.,substituting p-type transistors for n-type transistors, etc.)

In step S11, the reset gate RST, the floating gate FG, the secondholding unit MEM2, the first holding unit MEM1, and the transmissiongate TG are sequentially controlled to be turned on in this order, andthus the accumulated charge is released.

That is, as indicated by times t11, t21, t31, t41, and t51 of FIG. 5,the reset gate RST, the floating gate FG, the second holding unit MEM2,the first holding unit MEM1, and the transmission gate TG are controlledto be turned on (opened), and thus the accumulated charge is released,thereby executing a reset operation.

In step S12, as indicated by time t52 of FIG. 5, the transmission gateTG is turned off (closed).

In step S13, the turning off (closing) of the transmission gate TGstarts an accumulation operation of accumulating the charge generated bythe photodiode PD.

In step S14, as indicated by time t22 of FIG. 5, the floating gate FG isturned off (closed), and thus a state where the charge can be held inthe first holding unit MEM1 and the second holding unit MEM2 is set.

In step S15, at time t12 of FIG. 5, the reset gate RST is turned off(closed), and thus a state where the charge can be accumulated in thefloating diffusion FD is set.

As described above, as indicated by state St21 of FIG. 6, a state wherecharge is accumulated in the photodiode PD is set by a series ofprocesses of the steps S11 to S15. In addition, all the states St21 toSt25 of FIG. 6 show potential distribution as shown on the left side ofFIG. 2.

In step S16, as indicated by time t53 of FIG. 5, the transmission gateTG is controlled to be turned on, and thus the transmission gate TG isreleased (opened). As a result, as indicated by the state St22 of FIG.6, the charge accumulated in the photodiode PD is transmitted to thefirst holding unit MEM1 and the second holding unit MEM2.

In step S17, as indicated by time t54 of FIG. 5, the transmission gateTG is controlled to be turned off, and thus the transmission gate TG isclosed. As a result, as indicated by the state St23 of FIG. 6, thecharge accumulated in the photodiode PD is read out to the first holdingunit MEM1 and the second holding unit MEM2, and the charge is held inthe first holding unit MEM1 and the second holding unit MEM2. Inaddition, the state indicated by the state St23 is similar to the stateshown on the left side of FIG. 2.

In step S18, as indicated by time t61 of FIG. 5, the selection unit SELis turned on, and thus a state is set in which a voltage correspondingto the charge accumulated in the floating diffusion FD is output as apixel signal from the amplification unit AMP. However, in this stage,since charge is not accumulated in the floating diffusion FD, there isno pixel signal to be output from the amplification unit AMP.

In step S19, as indicated by the time t23 of FIG. 5, the floating gateFG is turned on (opened), and thus the charge held in the first holdingunit MEM1 and the second holding unit MEM2 is read out to the floatingdiffusion FD.

In step S20, at time t42 of FIG. 5, the first holding unit MEM1 isturned off, and thus the first holding unit MEM1 is closed. That is, asindicated by the state St24 of FIG. 6, the first holding unit MEM1 isturned off (closed), and thus the electric field in the electrode of thesecond holding unit MEM2 is strengthened. Accordingly, the inclinationof the potential becomes sharp, which leads to a state where the heldcharge has a tendency to be transmitted to the floating diffusion FD.

In step S21, at time t32 of FIG. 5, the second holding unit MEM2 isturned off, and thus the second holding unit MEM2 is closed. That is, asindicated by the state St25 of FIG. 6, the second holding unit MEM2 isturned off (closed), and thus a state where charge may not be held inany of the first holding unit MEM1 and the second holding unit MEM2 isset. Accordingly, the total amount of charge held is transmitted to thefloating diffusion FD.

In step S22, at the time t24 of FIG. 5, the floating gate FG is turnedoff(closed), and thus the transmission of the charge to the floatingdiffusion FD from the first holding unit MEM1 and the second holdingunit MEM2 is terminated. At this time, since the selection unit SEL isset to be in an on state by the process of step S18, the amplificationunit AMP amplifies a voltage supplied from the power source VDD inaccordance with the amount of charge transmitted to the floatingdiffusion FD and then outputs a pixel signal.

In step S23, as indicated by time t62 of FIG. 5, the selection unit SELis turned off, and thus the output from the amplification unit AMP isstopped.

As described above, charge transmitted from the photodiode PD is held intwo of the first holding unit MEM1 and the second holding unit MEM2, andthe charge is read out so that the second holding unit MEM2 is turnedoff after the first holding unit MEM1 is turned off. As a result, adistance at which the charge is transmitted is shortened by theelectrode of the second holding unit MEM2 which is half the size of aspace for holding the charge, thereby allowing a stronger electric fieldto be generated. Thus, the held charge is more reliably read out to thefloating diffusion FD.

Second Embodiment Configuration Example and Circuit ConfigurationExample of Solid-State Imaging Device According to Second Embodiment

In the above, an example in which a holding unit is divided into twopieces as a whole has been described, but the holding unit may bedivided into a greater number of pieces.

The left side of FIG. 7 shows a configuration example of a solid-stateimaging device in which a holding unit is divided into four pieces, andthe right side of FIG. 7 shows a circuit configuration example at thattime. In the configuration example of the solid-state imaging deviceshown on the left side of FIG. 7 and the circuit configuration exampleof the solid-state imaging device shown on the right side of FIG. 7,components having the same functions as those of the configurationexample of the solid-state imaging device of FIG. 2 and those of thecircuit configuration example of FIG. 3 will be given the same referencenumerals, signs and names, and the description thereof will beappropriately omitted.

That is, the configuration example and the circuit configuration exampleof the solid-state imaging device of FIG. 7 are different from theconfiguration example of the solid-state imaging device of FIG. 2 andthe circuit configuration example of FIG. 3 in that a first holding unitMEM1 to a fourth holding unit MEM4 each having a holding unit dividedinto four pieces are provided instead of the first holding unit MEM1 andthe second holding unit MEM2.

With such a configuration, as shown in FIG. 8, since each of the firstholding unit MEM1 to the fourth holding unit MEM4 occupies a quarter ofa transmission distance of charge which is held, it is possible togenerate a stronger electric field in each electrode and to morereliably read out the held charge to a floating diffusion FD. Inaddition, FIG. 8 shows an example of potential distribution in across-section taken along line A-B in the solid-state imaging device ofFIG. 7.

Charge Accumulation Transmission Process Using Solid-State ImagingDevice of FIG. 7

Next, a charge accumulation transmission process of the solid-stateimaging device of FIG. 7 will be described with reference to a flowchart of FIG. 9 and a timing chart of FIG. 10. In addition, FIG. 10shows a control state at a timing of the turning-on (High) orturning-off (Low) of each of the reset gate RST, the floating gate FG,the fourth holding unit MEM4 to the first holding unit MEM1, thetransmission gate TG, and the selection unit SEL from above.

In step S51, the reset gate RST, the floating gate FG, the fourthholding unit MEM4 to first holding unit MEM1, and transmission gate TGare sequentially controlled to be turned on in this order, and thus theaccumulated charge is released.

That is, as shown in FIG. 10, at times t101, t111, t121, t131, t141,t151, and t161, the reset gate RST, the floating gate FG, the fourthholding unit MEM4 to the first holding unit MEM1, and the transmissiongate TG are controlled to be turned on, and thus the accumulated chargeis released, thereby executing a reset operation.

In step S52, as indicated by time t162 of FIG. 10, the transmission gateTG is turned off(closed).

In step S53, the turning off (closing) of the transmission gate TGstarts an accumulation operation of accumulating the charge generated bythe photodiode PD.

In step S54, as indicated by time t112 of FIG. 10, the floating gate FGis turned off(closed), and thus a state where the charge can be held inthe first holding unit MEM1 to the second holding unit MEM4 is set.

In step S55, at time t102 of FIG. 10, the reset gate RST is turnedoff(closed), and thus a state where the charge can be accumulated in thefloating diffusion FD is set.

In step S56, as indicated by time t163 of FIG. 10, the transmission gateTG is controlled to be turned on, and thus the transmission gate TG isreleased(opened). As a result, the charge accumulated in the photodiodePD is transmitted to the first holding unit MEM1 to the fourth holdingunit MEM4.

In step S57, as indicated by time t164 of FIG. 10, the transmission gateTG is controlled to be turned off, and thus the transmission gate TG isclosed. As a result, the charge accumulated in the photodiode PD is readout to the first holding unit MEM1 to the fourth holding unit MEM4, andthe charge is held in the first holding unit MEM1 to the fourth holdingunit MEM4. In addition, the state at this time is the state shown inFIG. 8.

In step S58, as indicated by time t171 of FIG. 10, the selection unitSEL is turned on, and thus a state is set in which a voltagecorresponding to the charge accumulated in the floating diffusion FD isoutput as a pixel signal from the amplification unit AMP. However, inthis stage, since charge is not accumulated in the floating diffusionFD, there is no pixel signal output from the amplification unit AMP.

In step S59, as indicated by time t113 of FIG. 10, the floating gate FGis turned on(opened), and thus the charge held in the first holding unitMEM1 to the fourth holding unit MEM4 is read out to the floatingdiffusion FD.

In step S60, at time t152 of FIG. 10, the first holding unit MEM1 isturned off, and thus the first holding unit MEM1 is closed. That is, thefirst holding unit MEM1 is turned off(closed), and thus the electricfield in the electrode of each of the second holding unit MEM2 to thefourth holding unit MEM4 is strengthened. Accordingly, the inclinationof the potential becomes sharp, which leads to a state where the heldcharge has a tendency to be transmitted to the floating diffusion FD.

In steps S61 and S62, as indicated by times t142 and t132 of FIG. 10,the second holding unit MEM2 and the third holding unit MEM3 are turnedoff in stages, and the second holding unit MEM2 is closed, and then thethird holding unit MEM3 is closed. That is, the second holding unit MEM2and the third holding unit MEM3 are sequentially turned off(closed), andthus the electric fields in the electrodes of the third holding unitMEM3 and the fourth holding unit MEM4 are strengthened in stages.Accordingly, the inclination of the potential becomes sharp, which leadsto a state where the held charge has a tendency to be transmitted to thefloating diffusion FD.

In step S63, at time t122 of FIG. 10, the fourth holding unit MEM4 isturned off, and thus the fourth holding unit MEM4 is closed. That is,the fourth holding unit MEM4 is turned off(closed), and thus a statewhere charge may not be held in any of the first holding unit MEM1 tothe fourth holding unit MEM4 is set. Accordingly, the total amount ofcharge held is transmitted to the floating diffusion FD.

In step S64, at time t114 of FIG. 10, the floating gate FG is turnedoff(closed), and thus the transmission of the charge to the floatingdiffusion FD from the first holding unit MEM1 to the fourth holding unitMEM4 is terminated. At this time, since the selection unit SEL is set tobe in an on state by the process of step S58, the amplification unit AMPamplifies a voltage supplied from the power source VDD in accordancewith the amount of charge transmitted to the floating diffusion FD andthen outputs the voltage as a pixel signal.

In step S65, as indicated by time t172 of FIG. 10, the selection unitSEL is turned off, and thus the output from the amplification unit AMPis stopped.

As described above, charge transmitted from the photodiode PD is held infour of the first holding unit MEM1 to the fourth holding unit MEM4, andthe charge is read out so that the holding units up to the fourthholding unit MEM4 are sequentially turned off in stages after the firstholding unit MEM1 is turned off. As a result, a distance at which thecharge is transmitted is shortened to a quarter by an electrode of aquarter of a space for holding the charge, thereby allowing a strongerelectric field to be generated. Thus, the held charge is more reliablyread out to the floating diffusion FD.

In the above, an example in which an electrode constituting a holdingunit is divided into four pieces has been described, but the electrodemay be divided into a number other than four.

Third Embodiment Configuration Example and Circuit Configuration Exampleof Solid-State Imaging Device According to Third Embodiment

In the above, a description has been made of an example in which aholding unit is divided into four pieces to reduce a transmissiondistance of charge in an electrode constituting the holding unit to aquarter and an electric field is applied in stages to form a strongerelectric field in a transmission direction of the charge, therebyallowing the held charge to be more reliably transmitted. Incidentally,in the above, a description has been made of a configuration example inwhich divided electrodes are disposed so that the transmission gate TGis present on a straight line which is a division direction, but aconfiguration may be adopted in which the transmission gate TG isdisposed in a direction perpendicular to the division direction.

That is, the left side of FIG. 11 shows a configuration example of asolid-state imaging device in which divided electrodes are disposed sothat a transmission gate TG is disposed in a direction perpendicular toa division direction. In addition, the right side of FIG. 11 shows acircuit configuration example of the solid-state imaging device shown onthe left side of FIG. 11. In the solid-state imaging device of FIG. 11,components having the same functions as those of the solid-state imagingdevice of FIG. 7 will be given the same reference numerals, signs andnames, and the description thereof will be appropriately omitted.

That is, the solid-state imaging device of FIG. 11 is different from thesolid-state imaging device of FIG. 7 in that the transmission gate TG ofa photodiode PD is provided in a direction perpendicular to a directionin which a first holding unit MEM1 to a fourth holding unit MEM4 aredivided in a layout thereof. With such a configuration, as shown on theright side of FIG. 11, in the circuit configuration example, sources anddrains of the first holding unit MEM1 to the third holding unit MEM3 areconnected to each other in parallel.

With such a configuration, it is possible to ensure a wide transmissionpath, which makes it easier for charge to be transmitted.

That is, as shown on the upper left side of FIG. 12, a transmission pathr in the first holding unit MEM1 to the fourth holding unit MEM4 of thesolid-state imaging device of FIG. 7 is formed in a state where a marginhaving a distance d is generated in a direction perpendicular to atransmission direction. In FIG. 12, the upper left side shows layouts ofthe transmission gate TG and the first holding unit MEM1 to the fourthholding unit MEM4 of the solid-state imaging device of FIG. 7, and theupper right side shows layouts of the transmission gate TG and the firstholding unit MEM1 to the fourth holding unit MEM4 of the solid-stateimaging device of FIG. 11. In addition, the lower left side of FIG. 12shows a relationship between the second holding unit MEM2 in across-section taken along line A-A′ on the upper left side of FIG. 12and a cross-section of the transmission path r through which charge istransmitted, and the lower right side of FIG. 12 shows a relationshipbetween the second holding unit MEM2 in a cross-section taken along lineA-A′ of the upper right side of FIG. 12 and a cross-section of atransmission path r′ through which charge is transmitted.

That is, as shown on the lower left side of FIG. 12, the transmissionpath r desires a margin having a distance d in a direction horizontal tothe transmission direction. On the other hand, as shown on the upperright side of FIG. 12, when the transmission gate TG is disposed in adirection perpendicular to a direction in which the first holding unitMEM1 to the fourth holding unit MEM4 are divided, one end of the secondholding unit MEM2 comes into contact with the transmission gate TG asshown on the lower right side of FIG. 12. Thus, it is possible toinclude an end having one distance d as a portion of the transmissionpath. Accordingly, the transmission path r′ is configured to be thickerthan the transmission path r by one distance d.

As a result, the transmission path r′ configured to be wide and thickmakes it easier for charge to be transmitted, and thus it is possible tomore reliably transmit held charge to a floating diffusion FD.

Fourth Embodiment Circuit Configuration Example of Solid State ImagingDevice According to Fourth Embodiment

In the above, a description has been made of an example in which eachsolid-state imaging device outputs a pixel signal of one pixel. However,for example, the amount of charge output from photodiodes of pixels maybe set to the amount of charge capable of being held in a portion ofdivided holding units, and charge from the plurality of photodiodes maybe added (summed) and then output.

FIG. 13 shows a circuit configuration example of a solid-state imagingdevice in which charge supplied from photodiodes of four pixels is addedand then output. In the circuit configuration example of FIG. 13,components having the same functions as those of the circuitconfiguration of FIG. 7 will be given the same reference numerals, signsand names, and the description thereof will be appropriately omitted.

That is, the circuit configuration example of FIG. 13 is different fromthe circuit configuration example of FIG. 7 in that charge accumulatedin photodiodes PD of solid-state imaging devices of four pixels is addedand is then output by an amplification unit AMP. In FIG. 13, aconfiguration is adopted in which the configurations of the solid-stateimaging devices of four pixels are combined, and thus components havingthe same function will be discriminated by assigning signs of 1 to 4 tothe ends thereof. However, when it is not necessary to specially performdiscrimination, the ends will not be given numbers.

In more detail, provided are transmission gates TG1 to TG4, firstholding units MEM1-1 to MEM1-4, second holding units MEM2-1 to MEM2-4,third holding units MEM3-1 to MEM3-4, fourth holding units MEM4-1 toMEM4-4, and floating gates FG1 to FG4 which correspond to respectivephotodiodes PD1 to PD4 of four pixels. Further, output sides of thefloating gates FG1 to FG4 are connected to a reset gate RST and anamplification unit AMP in a state where all outputs are added by anaddition unit SUM. The “addition unit SUM” used herein is substantiallya floating diffusion FD which is shared by four pixels. Charge is readout to the floating diffusion FD, which is shared, from the floatinggates FG1 to FG4 and is then added.

In addition, although not shown in the drawing, the solid-state imagingdevice is configured such that the reset gate RST, the amplificationunit AMP, the selection unit SEL, and the addition unit SUM (floatingdiffusion FD) of FIG. 7 are shared by the transmission gates TG1 to TG4,the first holding units MEM1-1 to MEM1-4, the second holding unitsMEM2-1 to MEM2-4, the third holding units MEM3-1 to MEM3-4, the fourthholding units MEM4-1 to MEM4-4, and the floating gates FG1 to FG4 offour pixels.

With such a configuration, a timing when each of the floating gates FG1to FG4 is turned on or turned off is controlled, and thus it is possibleto add charge of four pixels using the addition unit SUM and then outputthe charge to the amplification unit AMP or to output the chargeindividually. In this example, although four pixels are added, othernumbers of pixels may be added.

Thinning Read-Out

As described above, it is possible to reduce the degradation of a pixelsignal and to realize thinning read-out at a high speed by using aconfiguration in which charge of a plurality of pixels can be added andthen output.

In the thinning read-out, for example, a so-called thinning process ofsimply reading out a pixel signal from only a quarter of all pixels, asimple addition process of reading out and simply adding a quarter ofall pixels, a pixel output quarter addition process of reading out onlya quarter (evenly reading out a quarter) of each charge of a quarter ofall pixels, and the like are considered. FIG. 14 is a diagram showingcomparisons between a total pixel read-out process of individuallyperforming read-out on each pixel, the thinning process, the simpleaddition process, and the pixel output quarter addition process.

In FIG. 14, it is assumed that four pixels of which the charge is addedare arranged in a Bayer array which is constituted by sixteen pixels of4 pixels×4 pixels, for example, as shown by the respective pixels on theupper stage. In FIG. 14, squares indicated by “R”, “B”, “Gr”, and “Gb”show a red pixel, a blue pixel, a green pixel on a line in which a redpixel is disposed, and a green pixel on a line in which a blue pixel isdisposed. Further, FIG. 14 shows cases of a total pixel read-outprocess, a thinning process, a simple addition process, and a pixeloutput quarter addition process from the left, and shows patterns ofpixels that are read out, a relationship between the amount of light perunit area and the number of output electrons, and a relationship betweenthe amount of light per one pixel and the number of output electronsfrom above.

For example, as shown at a second position from the left of FIG. 14,when only four of sixteen pixels are read out by a thinning process, thenumber of output electrons with respect to the amount of light per onepixel is the same as that in the total pixel read-out process as shownon the lower stage of the second position from the left of FIG. 14.However, as shown on the middle stage of the second position from theleft of FIG. 14, the number of output electrons with respect to theamount of light per unit area is reduced. This is because alight-receiving area becomes smaller due to the thinning. In this case,it is easy to be influenced by low illuminance noise.

In addition, for example, as shown on the uppermost stage of a secondposition from the right of FIG. 14, in a case of the simple additionprocess of simply adding charge of a pixel of each color and thenreading out the charge like the green pixel Gr enclosed by a heavy line,output per one pixel is similar to that in a case where read-out isperformed individually as shown on the lower stage of the secondposition from the right of FIG. 14. However, as shown on the middlestage of the second position from the right of FIG. 14, comparing thenumber of output electrons with respect to the amount of light per unitarea with that in the case where read-out is performed individually,charge of one pixel may be simply quadrupled and then output, and thusmay reach the amount of saturation of the amplification unit AMP, or astate where charge may not be accumulated in the floating diffusion FDis set. As a result, there is a concern that an appropriate signal maynot be output.

Consequently, in the solid-state imaging device of FIG. 13, as shown onthe uppermost stage of the rightmost side of FIG. 14, for example, onlycharge held in any one of a first holding unit MEM1 to a fourth holdingunit MEM4 of the green pixel Gr is extracted so that charge per onepixel is evened off to a quarter and the charge evened off to a quarteris added by four pixels. With such a process, the number of outputelectrons with respect to the amount of light per one pixel is a quarterof that in a case where read-out is performed individually. However,since the number of output electrons with respect to the amount of lightper unit area are added in the state of a quarter even when each pixelhas a maximum value, the added charge is only set to have a maximumvalue for one pixel. For this reason, since charge of four pixels issimultaneously read out, it is possible to increase a read-out speed. Inaddition, since the light-receiving area itself is not reduced, it ispossible to reduce the influence of low illuminance noise.

Individual Charge Accumulation Transmission Process for Each Pixel UsingSolid-State Imaging Device of FIG. 13

Next, an individual charge accumulation transmission process for eachpixel using the solid-state imaging device of FIG. 13 will be described.In addition, a charge accumulation transmission process of the totalpixel read-out process is essentially performed by repeating the processdescribed above with reference to the flow chart of FIG. 9 in pixelunits. However, in a case of the solid-state imaging device of FIG. 13,the floating gates FG1 to FG4 are individually turned on at differenttimings, and thus charge is transmitted to the floating diffusion FD foreach pixel, and then a pixel signal is output from the amplificationunit AMP.

That is, the processes of times t113 to t113′ of FIG. 15 areindividually repeated at different timings, with respect to four pixels.That is, in a timing chart of FIG. 15, a waveform of the floating gateFG in the timing chart of FIG. 10 is shown as a waveform of the floatinggate FG1, and a waveform of the floating gate FG2 is shown thereunder.Further, waveforms of the fourth holding unit MEM4 to the first holdingunit MEM1 and the transmission gate TG are shown as waveforms of thefourth holding unit MEM4-1 to the first holding unit MEM1-1 and thetransmission gate TG1.

That is, the fourth holding unit MEM4-1 to the first holding unit MEM1-1corresponding to the photodiode PD1 are sequentially turned off in theorder of time t152, time t142, time t132, and time t122 after thefloating gate FG1 is turned on at the time t113, and thus held charge istransmitted to the floating diffusion FD. The floating gate FG1 isturned off at time t114, and thus the transmission of charge of thephotodiode PD1 is completed, and an output as a pixel signal isobtained.

Thereafter, at the time t113′, the floating gate FG2 corresponding tothe photodiode PD2 is turned on, and thus the fourth holding unit MEM4-2to the first holding unit MEM1-2 corresponding to the photodiode PD1 areturned off at intervals similar to those of the fourth holding unitMEM4-1 to the first holding unit MEM1-1 corresponding to a pixel P1. Attime t114′, the floating gate FG2 is turned off, and thus thetransmission of charge of the photodiode PD2 is completed, and an outputas a pixel signal is obtained.

Although not shown in the drawing, a similar process is repeated withrespect to the floating gates FG3 and FG4, and thus pixel signals ofpixels P3 and P4 are sequentially output.

With this process, it is possible to read out a pixel signal, forexample, using the above-described total pixel read-out process as shownon the leftmost side of FIG. 14.

Charge Accumulation Transmission Process Through Addition for Every FourPixels Using Solid-State Imaging Device of FIG. 13

Next, a charge accumulation transmission process through addition forevery four pixels using the solid-state imaging device of FIG. 13 willbe described with reference to the flow chart of FIG. 16 and the timingchart of FIG. 17. In this example, regarding each of four pixels, chargesupplied through the transmission gate TG is held in only the firstholding unit MEM1 among the first holding unit MEM1 to the fourthholding unit MEM4 of each of the photodiodes PD1 to PD4, and the heldcharge is transmitted to the floating diffusion FD by the turning-on orturning-off of the floating gate FG. FIG. 17 shows a control state at atiming of the turning-on (High) or turning-off (Low) of each of thereset gate RST, the floating gates FG1 to FG4, the fourth holding unitMEM4 to the first holding unit MEM1 (each of which corresponds to fourpixels), the transmission gates TG1 to TG4, and the selection unit SELfrom above. Therefore, all of these are processes that aresimultaneously performed in four pixels, except for the control statesof the reset gate RST and the selection unit SEL.

That is, in step S51, the reset gate RST, the floating gate FG, thefourth holding unit MEM4 to the first holding unit MEM1, and thetransmission gate TG are sequentially controlled to be turned on in thisorder, and are then turned off in the reverse order after theaccumulated charge is released, and thus a reset operation is executed.

That is, as shown in FIG. 17, at times t201, t211, t221, t231, t241,t251, and t261, the reset gate RST, the floating gates FG1 to FG4, thefourth holding unit MEM4 to the first holding unit MEM1, and thetransmission gates TG1 to TG4 are controlled to be turned on, and thusthe accumulated charge is released. Further, thereafter, at times t262,t252, t242, t232, t222, t212, and t202, an operation of resetting thetransmission gates TG1 to TG4, the fourth holding unit MEM4 to the firstholding unit MEM1, the reset gate RST, and the floating gates FG1 to FG4is executed in the reverse order to the above-described order. Thus, thereset gate RST is turned off, and thus a state where the charge can beaccumulated in the floating diffusion FD is set.

In step S102, an operation of accumulating charge generated by thephotodiodes PD of the pixels P1 to P4 is started.

In step S103, as indicated by time t263 of FIG. 17, the transmissiongate TG is controlled to be turned on, and thus the transmission gate TGis released (opened). As a result, a state where the charge accumulatedin the photodiode PD can be transmitted to the first holding unit MEM1is set.

In step S104, as indicated by time t253 of FIG. 17, the first holdingunit MEM1 is turned on (opened). Thus, the first holding unit MEM1 isset to a state where the charge accumulated in the photodiode PD can beheld therein. That is, since the transmission gate TG is released(opened) by the previous process, the charge accumulated in thephotodiode PD is transmitted and is then held in the first holding unitMEM1.

In step S105, as indicated by time t264 of FIG. 17, the transmissiongate TG is controlled to be turned off (closed). As a result of thisprocess, the transmission of the charge accumulated in the photodiode PDto the first holding unit MEM1 is terminated.

In step S106, as indicated by time t243 of FIG. 17, the second holdingunit MEM2 is controlled to be turned on (opened). As a result of thisprocess, the charge held in the first holding unit MEM1 is transmittedto the second holding unit.

In step S107, as indicated by time t271 of FIG. 17, the selection unitSEL is turned on, and thus a state is set in which a voltagecorresponding to the charge accumulated in the floating diffusion FD isoutput from the amplification unit AMP. However, in this stage, sincecharge is not accumulated in the floating diffusion FD, there is nopixel signal to be output from the amplification unit AMP.

In step S108, as indicated by time t213 of FIG. 17, the floating gatesFG1 to FG4 are turned on(opened), and thus the charge held in the fourthholding unit MEM4 is read out to the floating diffusion FD.

In step S109, as indicated by time t254 of FIG. 17, the first holdingunit MEM1 is turned off, and thus the first holding unit MEM1 is closed.That is, the first holding unit MEM1 is turned off(closed), and thus astate where the charge held in the first holding unit MEM1 istransmitted to the second holding unit MEM2 is set.

In step S110, as indicated by time t223 of FIG. 17, the fourth holdingunit MEM4 is turned on(opened), and thus a state where the chargeaccumulated in the third holding unit MEM3 can be received and then heldis set.

In step S111, as indicated by time t233 of FIG. 17, the third holdingunit MEM3 is turned on(opened), and thus the charge held in the secondholding unit MEM2 is transmitted to the floating diffusion FD throughthe third holding unit MEM3 and the fourth holding unit MEM4. At thistime, since the selection unit SEL is set to be in an on state by theprocess of step S107, the amplification unit AMP amplifies a voltagesupplied from the power source VDD in accordance with the amount ofcharge transmitted to the floating diffusion FD and then outputs a pixelsignal. At this time, the addition unit SUM, which is substantiallyconstituted by the floating diffusion FD, adds charge supplied from allthe solid-state imaging devices of the pixels P1 to P4 and then suppliesthe charge to the amplification unit AMP.

In step S112, as indicated by time t244 of FIG. 17, the second holdingunit MEM2 is turned off(closed), and thus an electric field according tothe third holding unit MEM3 and the fourth holding unit MEM4 isstrengthened. Accordingly, the held charge has a tendency to betransmitted to the floating diffusion FD.

In step S113, as indicated by time t234 of FIG. 17, the third holdingunit MEM3 is turned off(closed), and thus electric field intensity inthe fourth holding unit MEM4 is further strengthened. Accordingly, theheld charge has a tendency to be transmitted to the floating diffusionFD.

In step S114, as indicated by time t224 of FIG. 17, the fourth holdingunit MEM4 is turned off(closed).

In step S115, as indicated by time t214 of FIG. 17, the floating gatesFG1 to FG4 are controlled to be turned off(closed). As a result, thetransmission of the charge to the floating diffusion FD from the fourthholding unit MEM4 is terminated.

In step S116, as indicated by time t272 of FIG. 17, the selection unitSEL is turned off, and thus the output from the amplification unit AMPis stopped.

As described above, charge transmitted from the photodiode PD is held bythe amount of charge capable of being held in the first holding unitMEM1, and is sequentially transmitted to the second holding unit MEM2 tothe fourth holding unit MEM4, and is then read out to the floatingdiffusion FD. As a result, it is possible to transmit the charge to thefloating diffusion FD by an amount which is evened off to a quarter ofthe amount of charge capable of being held in the first holding unitMEM1 to the fourth holding unit MEM4, in units of a pixel.

In addition, the addition unit SUM constituted by the floating diffusionFD adds charge of the solid-state imaging devices of four pixels andthen supplies the charge to the amplification unit AMP. As a result, asdescribed above with reference to FIG. 14, it is possible tosimultaneously read out pixel signals of four pixels at a high speedwithout reducing the light-receiving area.

In the above, an example in which an electrode constituting a holdingunit is divided into four pieces has been described, but the electrodemay be divided into a number other than four.

Further, in the above, a description has been made of an example inwhich pixels accumulated by the first holding unit MEM1 are sequentiallytransmitted to the second holding unit MEM2 to the fourth holding unitMEM4 to thereby transmit charge by an amount which is evened off to aquarter of the amount of charge capable of being held as a whole, butonly charge held in the second holding unit MEM2 may be transmitted. Inthis case, since processes of step S104 and step S109 are skipped, astate where the first holding unit MEM1 is not released is set asindicated by times t253 to t254 of FIG. 17. In addition, as shown inFIG. 18, a timing when the second holding unit MEM2 is turned on andthen released, which is the process of step S106, is set to time t243′which is a timing between time t263 and time t264 when the transmissiongate TG is turned on and then accumulated charge is transmitted from thephotodiode PD. Thus, the charge held in the second holding unit MEM2 issequentially transmitted to the floating diffusion FD through the thirdholding unit MEM3, the fourth holding unit MEM4, and the floating gateFG.

In addition, it is possible to realize a case where only charge held inthe third holding unit MEM3 is transmitted through the fourth holdingunit MEM4 and the floating diffusion FD, in a similar manner.

Further, this is the same as in a case where only charge held in thefourth holding unit MEM4 is transmitted to the floating diffusion FD.That is, as shown in FIG. 19, a timing when the fourth holding unit MEM4is turned on and then released may be set to time t223′ which is atiming between the time t263 and the time t264 when the transmissiongate TG is released. In addition, as a matter of course, all of thefirst holding unit MEM1 to the third holding unit MEM3 are not turned onafter a reset operation.

As described above, it is possible to transmit charge to the floatingdiffusion FD by an amount which is evened off to a quarter of the amountof charge capable of being held in any one of the first holding unitMEM1 to the fourth holding unit MEM4 and to simultaneously read outpixel signals of four pixels at a high speed without reducing thelight-receiving area.

Fifth Embodiment Configuration Example and Circuit Configuration Exampleof Solid-State Imaging Device According to Fifth Embodiment

In the above, a description has been made of an example in which allgates are opened to discharge charge accumulated in the photodiode PD tothe reset drain RST Drain and then the accumulation of charge is startedto sequentially transmit the accumulated charge to the floatingdiffusion FD through the first holding unit MEM1 to the fourth holdingunit MEM4. However, in order to reset the charge accumulated in thephotodiode PD, a separate gate may be provided so that the charge may bereset while being transmitted in a first holding unit MEM1 to a fourthholding unit MEM4.

FIG. 20 shows a configuration example and a circuit configurationexample of a solid-state imaging device in which a global reset gate PGcapable of directly discharging accumulated charge to a reset drain RSTDrain is provided in a photodiode PD. In the configuration example andthe circuit configuration example of the solid-state imaging device ofFIG. 20, components having the same functions as the components in theconfiguration example of the solid-state imaging device of FIG. 2 andthe circuit configuration example of FIG. 3 will be given the samereference numerals, signs and names, and the description thereof will beappropriately omitted.

That is, the solid-state imaging device of FIG. 20 is different from thesolid-state imaging devices of FIG. 2 and FIG. 3 in that the globalreset gate PG is newly provided in the photodiode PD.

For example, the global reset gate PG is a hole-accumulation diode(HAD). The global reset gate has a function similar to that of anoverflow discharge portion OFB as shown in FIG. 21 and directlydischarges charge accumulated in the photodiode PD to the reset drainRST Drain adjacent thereto. That is, the global reset gate PG maydischarge charge remaining in the photodiode PD to the reset drain RSTDrain while the charge is transmitted in the first holding unit MEM1 tothe fourth holding unit MEM4, thereby completing the reset operation. Inaddition, FIG. 21 shows potential distribution in a cross-section takenalong line B-B′ of FIG. 20.

Charge Accumulation Transmission Process Using Solid-State ImagingDevice of FIG. 20

Next, a charge accumulation transmission process of the solid-stateimaging device of FIG. 20 will be described with reference to a flowchart of FIG. 22 and a timing chart of FIG. 23. In FIG. 23, a waveformindicating a control state of the global reset gate PG is shown on thelowermost stage, in addition to the waveform of FIG. 5.

In step S131, a reset gate RST, a floating gate FG, the second holdingunit MEM2, and the first holding unit MEM1 are sequentially controlledto be turned on in this order, and thus the accumulated charge isreleased.

That is, as indicated by times t11, t21, t31, t41 of FIG. 23, the resetgate RST, the floating gate FG, the second holding unit MEM2, and thefirst holding unit MEM1 are controlled to be turned on, and thus theaccumulated charge is released, thereby executing a reset operation.

In step S132, as indicated by time t22 of FIG. 23, the floating gate FGis turned off, and thus a state where the charge can be held in thefirst holding unit MEM1 and the second holding unit MEM2 is set.

In step S133, at time t12 of FIG. 23, the reset gate RST is turned off,and thus a state where the charge can be accumulated in the floatingdiffusion FD is set.

In step S134, as indicated by time t53 of FIG. 23, the transmission gateTG is controlled to be turned on, and thus the transmission gate TG isreleased. In the previous charge accumulation transmission process, theaccumulation of the charge of the photodiode PD is completed byprocesses of steps S142 and S143 to be described later, and thus thecharge accumulated in the photodiode PD is transmitted to the firstholding unit MEM1 and the second holding unit MEM2. In addition, herein,waveforms at times t51 to t52 in the timing chart of FIG. 5 are notpresent. That is, in the solid-state imaging device of FIG. 22, sincethe global reset gate PG is present, the transmission gate TG is notdesired to be released.

In step S135, as indicated by time t54 of FIG. 23, the transmission gateTG is controlled to be turned off, and thus the transmission gate TG isclosed. As a result, the charge accumulated in the photodiode PD is readout to the first holding unit MEM1 and the second holding unit MEM2, andthe charge is held in the first holding unit MEM1 and the second holdingunit MEM2.

In step S136, as indicated by time t301 of FIG. 23, the global resetgate PG is controlled to be turned on, and the charge remaining in thephotodiode PD is discharged to the reset drain RST Drain.

In step S137, as indicated by time t61 of FIG. 23, a selection unit SELis turned on, and thus a state is set in which a voltage correspondingto the charge accumulated in the floating diffusion FD is output as apixel signal from an amplification unit AMP. However, in this stage,since charge is not accumulated in the floating diffusion FD, there isno pixel signal to be output from the amplification unit AMP.

In step S138, as indicated by time t23 of FIG. 23, the floating gate FGis turned on and then released, and thus the charge held in the firstholding unit MEM1 and the second holding unit MEM2 is read out to thefloating diffusion FD.

In step S139, at time t42 of FIG. 23, the first holding unit MEM1 isturned off, and thus the first holding unit MEM1 is closed. That is, thefirst holding unit MEM1 is turned off(closed), and thus an electricfield in an electrode of the second holding unit MEM2 is strengthened.Accordingly, the inclination of the potential becomes sharp, which leadsto a state where the held charge has a tendency to be transmitted to thefloating diffusion FD.

In step S140, at time t32 of FIG. 23, the second holding unit MEM2 isturned off, and thus the second holding unit MEM2 is closed. That is,the second holding unit MEM2 is turned off(closed), and thus a statewhere charge may not be held in any of the first holding unit MEM1 andthe second holding unit MEM2 is set. Accordingly, the total amount ofcharge held is transmitted to the floating diffusion FD.

In step S141, at time t24 of FIG. 23, the floating gate FG is turnedoff(closed), and thus the transmission of the charge to the floatingdiffusion FD from the first holding unit MEM1 and the second holdingunit MEM2 is terminated. At this time, since the selection unit SEL isset to be in an on state by the process of step S137, the amplificationunit AMP amplifies a voltage supplied from a power source VDD inaccordance with the amount of charge transmitted to the floatingdiffusion FD and then outputs a pixel signal.

In step S142, as indicated by time t302 of FIG. 23, the global resetgate PG is turned off(closed).

In step S143, since the global reset gate PG and the transmission gateTG are turned off(closed), the photodiode PD starts to accumulatecharge.

In step S144, as indicated by time t62 of FIG. 23, the selection unitSEL is turned off, and thus the output from the amplification unit AMPis stopped.

Thereafter, since the reset operation has been already completed in thephotodiode PD, it is possible to accumulate charge generated byphotoelectric conversion according to light reception during the resetoperation of the first holding unit MEM1 and the second holding unitMEM2.

As a result, the reset operation of the photodiode PD and thetransmission of the charge to the floating diffusion FD in the firstholding unit MEM1 and the second holding unit MEM2 are processed inparallel, and thus it is possible to realize the overall operation at ahigh speed and to improve a frame rate.

Sixth Embodiment Configuration Example and Circuit Configuration Exampleof Solid-State Imaging Device According to Sixth Embodiment

In the above, description has been made of an example in which theholding unit holding charge transmitted from the photodiode PD isconstituted by electrodes which are equally divided, but the holdingunit may be constituted by electrodes which are unequally divided.

The left and right sides of FIG. 24 show a configuration example and acircuit configuration example of a solid-state imaging device thatincludes a first holding unit MEM1, a second holding unit MEM2, and athird holding unit MEM3 each which is constituted by electrodes whichare unequally divided. In addition, in the configuration of thesolid-state imaging device of FIG. 24, components having the samefunctions as those of the solid-state imaging device of FIG. 11 will begiven the same reference numerals, signs and names, and the descriptionthereof will be appropriately omitted.

That is, the solid-state imaging device of FIG. 24 is different from thesolid-state imaging device of FIG. 11 in that electrodes are divided tohave unequal areas in three holding units. That is, as shown on the leftside of FIG. 24, the first holding unit MEM1 and the second holding unitMEM2 are divided to have areas which are substantially equal to eachother. However, the third holding unit MEM3 has an area twice as largeas those of the first holding unit MEM1 and the second holding unitMEM2.

In addition, as shown on the right side of FIG. 24, a photodiode PD1 isprovided with a first holding unit MEM1-1 to a third holding unitMEM3-1, and a floating gate FG1. In addition, a photodiode PD2 isprovided with a first holding unit MEM1-2 to a third holding unitMEM3-2, and a floating gate FG2. Further, a photodiode PD3 is providedwith a first holding unit MEM1-3 to a third holding unit MEM3-3, and afloating gate FG3. In addition, a photodiode PD4 is provided with afirst holding unit MEM1-4 to a third holding unit MEM3-4, and a floatinggate FG4.

Further, an output of each of floating gates FG1 to FG4 is connected toan addition unit SUM constituted by a floating diffusion FD. Theaddition unit SUM adds charge serving as outputs of the floating gatesFG1 to FG4 and then outputs the charge to a reset gate RST and anamplification unit AMP.

For example, as shown on the left side of FIG. 24, a third holding unitMEM3′ constituted by an electrode having a relatively large area may bedisposed in a range in which charge has a tendency to be transmittedwith a short moving distance of the charge close to the floating gate FGwhich is a transmission destination. On the other hand, in a range inwhich charge has a tendency not to be transmitted with a long movingdistance of the charge to the floating gate FG which is a transmissiondestination, the first holding unit MEM1 and the second holding unitMEM2 each which is constituted by an electrode having a relatively smallarea may be disposed. With such an arrangement, a strong electric fieldmay be locally applied by a small electrode for a long range of adistance at which charge is to be transmitted, and the amount of chargecapable of being transmitted by one control operation of turning-on orturning-off may be increased by a large electrode for a short range of adistance at which charge is to be transmitted.

In addition, the charge accumulation transmission process of thesolid-state imaging device of FIG. 24 is similar to the processdescribed with reference to the flow chart of FIG. 9 or FIG. 16excluding the process regarding the second holding unit MEM2 or thethird holding unit MEM3 in the first holding unit MEM1 to the fourthholding unit MEM4, and thus the description thereof will be omittedhere.

Seventh Embodiment Configuration Example and Circuit ConfigurationExample of Solid-State Imaging Device According to Seventh Embodiment

In the above, a description has been made of an example in which thetransmission of charge accumulated in the photodiode PD to the holdingunit is controlled by the transmission gate TG. However, since thecharge accumulated in the photodiode PD may be able to be transmitted tothe holding unit, the transmission gate TG may be omitted and thetransmission may be able to be directly controlled by turning-on orturning-off of the holding unit.

The right side of FIG. 25 shows a configuration example of a solid-stateimaging device in which a transmission gate TG is omitted and thetransmission of charge accumulated in a photodiode PD can be controlledby turning-on or turning-off of a first holding unit MEM1. In addition,the left side of FIG. 25 shows potential distribution in a cross-sectiontaken along line A-B which is indicated by a dotted line of the rightside of FIG. 25. In the configuration of the solid-state imaging deviceof FIG. 25, components having the same functions as those of thesolid-state imaging device of FIG. 20 will be given the same referencenumerals, signs and names, and the description thereof will beappropriately omitted.

That is, the solid-state imaging device of FIG. 25 is different from thesolid-state imaging device of FIG. 20 in that the photodiode PD isdisposed in a direction in which the first holding unit MEM1 and thesecond holding unit MEM2 are divided in FIG. 20, whereas the photodiodePD is disposed in a direction perpendicular to the direction in whichthe first holding unit MEM1 and a second holding unit MEM2 are dividedin FIG. 25. Further, there is a difference in that a transmission gateTG is omitted and a global reset gate PG is connected to a reset drainRST Drain in the same pixel. Therefore, in the drawing on the left sideof FIG. 25, the reset drain RST Drain on the left side is identical tothat on the right side. Further, the first holding unit MEM1 and thesecond holding unit MEM2 of FIG. 25 have a function with an operation ofthe transmission gate TG.

In more detail, the first holding unit MEM and the second holding unitMEM2 of FIG. 25 are controlled by three values, for example, +6 V, 0 V,and −3 V. In this case, when the voltage is +6 V, the first holding unitMEM and the second holding unit MEM2 release a gate at a boundary withthe photodiode PD to transmit accumulated charge to themselves. Inaddition, when the voltage is 0 V, the first holding unit MEM and thesecond holding unit MEM2 are set to be in a state where the gate at theboundary with the photodiode PD is closed and the charge can be held.Further, when the voltage is −3 V, the first holding unit MEM and thesecond holding unit MEM2 are set to be in a closed state, and thustransmit held charge to the floating diffusion FD through the floatinggate FG.

Charge accumulation transmission process Using Solid-State ImagingDevice of FIG. 25

Next, a charge accumulation transmission process of the solid-stateimaging device of FIG. 25 will be described with reference to a flowchart of FIG. 26 and a timing chart of FIG. 27. FIG. 27 shows a controlstate at a timing of the turning-on (High) or turning-off (Low) of eachof the reset gate RST, the floating gate FG, the selection unit SEL, andthe global reset gate PG. Further, FIG. 25 shows control states of H(High) equivalent to +6 V, M (Middle) equivalent to 0 V, and L (Low)equivalent to −3 V which are described above in the second holding unitMEM2 and the first holding unit MEM1.

In addition, this process is based on the premise that the global resetgate PG is turned on and then released to discharge charge of thephotodiode PD to the reset drain RST Drain and that the global resetgate is turned off to set a state where the charge can be accumulated,by the previous process.

In step S171, the reset gate RST, the floating gate FG, the secondholding unit MEM2, and the first holding unit MEM1 are sequentiallycontrolled to be turned on, and thus held charge is released.

That is, as shown in FIG. 27, at times t11 and t21, the reset gate RSTand the floating gate FG are turned on. Further, at times t31 and t41,the second holding unit MEM2 and the first holding unit MEM1 arecontrolled to be in the state of Middle. In this state, the first andsecond holding unit MEM1 and MEM2 are closed with respect to thephotodiode PD but are open with respect to the reset drain RST Drain,and thus the accumulated charge in the first and second holding unitMEM1 and MEM2 is released through the reset drain RST Drain, therebyexecuting a reset operation for the floating diffusion FD and the firstand second holding unit MEM1 and MEM2.

In step S172, as indicated by time t22 of FIG. 27, the floating gate FGis turned off, and thus a state where the charge can be held in thefirst holding unit MEM1 and the second holding unit MEM2 is set.

In step S173, at time t12 of FIG. 27, the reset gate RST is turned off,and thus a state where the charge can be accumulated in the floatingdiffusion FD is set.

In step S174, as indicated by time t321 of FIG. 27, the first holdingunit MEM1 and the second first holding unit MEM2 are controlled to be inthe state of High, and thus the boundary with the photodiode PD isreleased (opened). As a result, the charge accumulated in the photodiodePD is transmitted to the first holding unit MEM1 and the second holdingunit MEM2.

In step S175, as indicated by time t322 of FIG. 27, the first holdingunit MEM1 and the second first holding unit MEM2 are controlled to be inthe state of Middle, and thus the boundary with the photodiode PD isclosed. As a result, the transmission of the charge from the photodiodePD is stopped.

In step S176, as indicated by time t301 of FIG. 27, the global resetgate PG is turned on(opened), and thus the charge accumulated in thephotodiode PD is discharged to the reset drain RST Drain.

In step S177, as indicated by time t61 of FIG. 27, the selection unitSEL is turned on, and thus a state is set in which a voltagecorresponding to the charge accumulated in the floating diffusion FD isoutput from the amplification unit AMP. However, in this stage, sincecharge is not accumulated in the floating diffusion FD, there is nopixel signal to be output from the amplification unit AMP.

In step S178, as indicated by time t23 of FIG. 27, the floating gate FGis turned on(opened), and thus the charge held in the first holding unitMEM1 and the second holding unit MEM2 is read out to the floatingdiffusion FD.

In step S179, at time t42 of FIG. 27, the first holding unit MEM1 is setto be in the state of Low, and thus the first holding unit MEM1 isclosed. That is, the first holding unit MEM1 is set to be in the stateof Low(closed), and thus the electric field in the electrode of thesecond holding unit MEM2 is strengthened. Accordingly, the inclinationof the potential becomes sharp, which leads to a state where the heldcharge has a tendency to be transmitted to the floating diffusion FD.

In step S180, at time t32 of FIG. 27, the second holding unit MEM2 isset to be in the state of Low, and thus the second holding unit MEM2 isclosed. That is, the second holding unit MEM2 is set to be in the stateof Low and closed, and thus a state where charge may not be held in anyof the first holding unit MEM1 and the second holding unit MEM2 is set.Accordingly, the total amount of charge held is transmitted to thefloating diffusion FD.

In step S181, at time t24 of FIG. 27, the floating gate FG is turnedoff(closed), and thus the transmission of the charge to the floatingdiffusion FD from the first holding unit MEM1 and the second holdingunit MEM2 is terminated. At this time, since the selection unit SEL isset to be in an on state by the process of step S177, the amplificationunit AMP amplifies a voltage supplied from a power source VDD inaccordance with the amount of charge transmitted to the floatingdiffusion FD and then outputs a pixel signal.

In step S182, as indicated by time t302 of FIG. 27, the global resetgate PG is turned off(closed).

In step S183, the photodiode PD is set to be in a state where the chargecan be accumulated by the process of step S182.

In step S184, as indicated by time t62 of FIG. 27, the selection unitSEL is turned off, and thus the output from the amplification unit AMPis stopped.

As described above, the first holding unit MEM1 and the second holdingunit MEM2 can be provided with the function of the transmission gate TG,and thus it is possible to hold charge transmitted from the photodiodePD in two of the first holding unit MEM1 and the second holding unitMEM2 even when the transmission gate TG is omitted and to read out thecharge so that the second holding unit MEM2 is turned off after thefirst holding unit MEM1 is turned off. As a result, even in aconfiguration in which the transmission gate TG is omitted, the heldcharge is more reliably read out to the floating diffusion FD.

Electrode Configuration

Next, electrode configurations of the first holding unit MEM1 and thesecond holding unit MEM2 in the solid-state imaging device of FIG. 25will be described.

When the first holding unit MEM1 and the second holding unit MEM2 areconfigured as shown in FIG. 25, a wiring is connected as shown in FIG.28 in the related art. In FIG. 28, a left side shows a top view, amiddle side shows a cross-sectional view taken along line A-A′ of theleft side, and a right side shows a cross-sectional view taken alongline B-B′ of the left side.

That is, the first holding unit MEM1 is constituted by a stack of a gateelectrode GD1 and gate oxide film GOX1, and the second holding unit MEMis constituted by a stack of a gate electrode GD2 and gate oxide filmGOX2. A wiring L1 is connected to the gate electrode GD1 through acontact CT11, and the turning-on and turning-off of the first holdingunit MEM1 are controlled by power supplied from the wiring L1. Inaddition, a wiring L2 is connected to the gate electrode GD2 through acontact CT12, and the turning-on and turning-off of the second holdingunit MEM2 are controlled by power supplied from the wiring L2.Incidentally, a light shielding film F is further connected to the gateelectrode GD1 of the first holding unit MEM1 through a contact CT13.

That is, the light shielding film F is formed of a metal, and thus it ispossible to omit the wiring L1 by using the light shielding film Finstead of the wiring L1.

FIG. 29 shows the configuration of a solid-state imaging device in whicha wiring is omitted by using the light shielding film F instead of thewiring L1. That is, in this example, the light shielding film F isconnected to the first holding unit MEM1 through a contact CT31. Inaddition, a wiring L31 is connected to the second holding unit MEM2through a contact CT32. In this manner, the light shielding film Ffunctions as a portion of a wiring, and thus it is possible to increasethe amount of light incident on the photodiode PD, and the degree offreedom in routing the wiring is improved.

In addition, a memory gate material constituting the gate oxide film GOXis a material in which high dielectric materials such as SiN, HfO₂, andTaO₂ are laminated in addition to SiO₂.

Further, examples of an electrode material constituting the gateelectrode GD include Poly Si, PDAS, a metal material, and the like. Inaddition, it is possible to reduce the thickness of the light shieldingfilm by adopting the metal material as the electrode material. Inaddition, W, Mo, Al, Cu, and the like which have a high extinctioncoefficient are preferably used as the material of the light shieldingfilm.

In addition, such a wiring configuration may be applied to theabove-described solid-state imaging devices according to the firstembodiment to the sixth embodiment.

In addition, the embodiments of the present disclosure are not limitedto the above-described embodiments, and various modifications can bemade without departing from the scope of the present disclosure.

For example, the steps described in the above-described flow charts canbe performed not only using one device but also using a plurality ofdevices for sharing.

Further, when one step includes a plurality of processes, the pluralityof processes included in the one step can be performed not only usingone device but also using a plurality of devices for sharing.

In addition, the present disclosure can also adopt the followingconfiguration.

(1) A solid-state imaging device including:

a photodiode that receives light in pixel units and generates charge byphotoelectric conversion; and

a holding unit that includes electrodes divided into a plurality ofpieces and temporarily holds the charge generated by the photodiode,

wherein the holding unit sequentially switches turning-on or turning-offof the divided electrodes to thereby transmit the held charge to afloating diffusion.

(2) The solid-state imaging device according to (1), wherein thesolid-state imaging device is a global shutter type solid-state imagingdevice.

(3) The solid-state imaging device according to (1) or (2), furtherincluding an addition unit that adds the charge transmitted from theholding units of the plurality of pixels,

wherein charge accumulated in a portion of the electrodes divided into aplurality of pieces is transmitted to the floating diffusion, and

wherein the addition unit adds the charge accumulated in the portion ofthe electrodes divided into a plurality of pieces by the plurality ofpixels and then transmits the charge.

(4) The solid-state imaging device according to any one of (1) and (3),further including a read-out electrode which is constituted by anelectrode that controls the transmission of the charge generated by thephotodiode to the holding unit,

wherein the read-out electrode is configured in a directionperpendicular to a division direction of the electrodes divided into aplurality of pieces, which constitute the holding unit.

(5) The solid-state imaging device according to any one of (1) to (4),wherein the plurality of divided electrodes constituting the holdingunit are divided so as to have substantially equal areas.

(6) The solid-state imaging device according to any one of (1) to (4),wherein the plurality of divided electrodes constituting the holdingunit are divided so as to have unequal areas.

(7) The solid-state imaging device according to any one of (1) to (6),wherein the holding unit has a function of transmitting the chargegenerated by the photodiode to itself.

(8) The solid-state imaging device according to any one of (1) to (5),further including a global reset gate that controls turning-on orturning-off for directly discharging the charge of the photodiode to areset drain.

(9) The solid-state imaging device according to any one of (1) to (8),wherein the holding unit includes SiO₂, SiN, HfO₂, or TaO₂ and is formedby a stack thereof.

(10) The solid-state imaging device according to any one of (1) to (9),wherein a material of the electrode is a metal material including PolySi, PDAS, W, Mo, Al, or Cu.

(11) The solid-state imaging device according to any one of (1) to (10),

wherein the holding unit further includes a light-shielding unit, and

wherein any one of the electrodes divided into a plurality of pieces isshorted from the light-shielding unit.

(12) A method of operating a solid-state imaging device, the methodincluding:

causing a photodiode to receive light in pixel units and to generatecharge by photoelectric conversion; and

causing a holding unit with electrodes divided into a plurality ofpieces to temporarily hold the charge generated by the photodiode,

wherein the holding unit sequentially switches turning-on or turning-offof the divided electrodes to thereby transmit the held charge to afloating diffusion.

(13) An electronic apparatus having a solid-state imaging device, theelectronic apparatus including:

a photodiode that receives light in pixel units and generates charge byphotoelectric conversion; and

a holding unit that includes electrodes divided into a plurality ofpieces and temporarily holds the charge generated by the photodiode,

wherein the holding unit sequentially switches turning-on or turning-offof the divided electrodes to thereby transmit the held charge to afloating diffusion.

(14) The electronic apparatus according to (13), wherein the solid-stateimaging device is a global shutter type solid-state imaging device.

(15) The electronic apparatus according to (13) or (14), furtherincluding an addition unit that adds the charge transmitted from theholding units of the plurality of pixels,

wherein charge accumulated in a portion of the electrodes divided into aplurality of pieces is transmitted to the floating diffusion, and

wherein the addition unit adds the charge accumulated in the portion ofthe electrodes divided into a plurality of pieces by the plurality ofpixels and then transmits the charge.

(16) The electronic apparatus according to any one of (13) to (15),further including a read-out electrode which is constituted by anelectrode that controls the transmission of the charge generated by thephotodiode to the holding unit,

wherein the read-out electrode is configured in a directionperpendicular to a division direction of the electrodes divided into aplurality of pieces, which constitute the holding unit.

(17) The electronic apparatus according to any one of (13) to (16),wherein the plurality of divided electrodes constituting the holdingunit are divided so as to have substantially equal areas.

(18) The electronic apparatus according to any one of (13) to (16),wherein the plurality of divided electrodes constituting the holdingunit are divided so as to have unequal areas.

(19) The electronic apparatus according to any one of (13) to (19),wherein the holding unit has a function of transmitting the chargegenerated by the photodiode to itself.

(20) A method of operating an electronic apparatus having a solid-stateimaging device, the method including:

causing a photodiode to receive light in pixel units and to generatecharge by photoelectric conversion; and

causing a holding unit with electrodes divided into a plurality ofpieces to temporarily hold the charge generated by the photodiode,

wherein the holding unit sequentially switches turning-on or turning-offof the divided electrodes to thereby transmit the held charge to afloating diffusion.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

(21) An imaging device, comprising:

a plurality of pixels in a two-dimensional array, each including:

-   -   a photoelectric conversion element that converts incident light        into an electric charge; and    -   a charge holding element that receives the electric charge from        the photoelectric conversion element, and transfers the electric        charge to a corresponding floating diffusion,

wherein, for each of the plurality of pixels, the charge holding elementincludes a plurality of electrodes.

(22) The imaging device of any one of (21) through (37), furthercomprising:

a control circuit that controls operations of the plurality of pixels,

wherein the control circuit is configured to cause the charge holdingelement of a given pixel of the plurality of pixels to transfer theelectric charge held therein to the corresponding floating diffusion bysequentially supplying an OFF potential to the plurality of electrodesof the given pixel.

(23) The imaging device of any one of (21) through (37), furthercomprising:

a control circuit that controls operations of the plurality of pixels,

wherein the control circuit is configured to drive the plurality ofpixels to perform a global shutter imaging operation.

(24) The imaging device of any one of (21) through (37),

wherein the plurality of pixels are grouped into units each comprising jpixels, j being an integer greater than 1, where each of the pixels thatis included in a same unit corresponds to a same floating diffusion.

(25) The imaging device of any one of (21) through (37), furthercomprising:

a control circuit that controls operations of the plurality of pixels,

wherein the control circuit is configured to cause a given unit toperform an additive readout operation that includes transferring theelectric charges held in the respective charge holding elements of eachof the pixels of the given unit to the corresponding floating diffusionsuch that the corresponding floating diffusion adds together theelectric charges transferred from the pixels of the given unit.

(26) The imaging device of any one of (21) through (37), furthercomprising:

a control circuit that controls operations of the plurality of pixels,

wherein the control circuit is configured to cause a given unit toperform a partial additive readout operation including:

-   -   for each of the pixels of the given unit, turning on less than        all of the plurality of electrodes of the charge holding element        of the respective pixel while the charge holding element of the        respective pixel receives the electric charge from the        photoelectric conversion element of the respective pixel, and    -   transferring the electric charges held in the respective charge        holding elements of each of the pixels of the given unit to the        corresponding floating diffusion such that the corresponding        floating diffusion adds together the electric charges        transferred from the pixels of the given unit.

(27) The imaging device of any one of (21) through (37), furthercomprising:

a control circuit that controls operations of the plurality of pixels,

wherein the control circuit is configured selectively read out a givenunit according to one of a plurality of readout modes that the controlcircuit is configured to selectively switch between, the plurality ofreadout modes including:

-   -   an individual pixel readout mode in which the electric charge of        the charge holding element of each pixel of the given unit is        read out individually,    -   an additive readout mode in which the electric charge of the        charge holding element of each pixel of the given unit is added        together by the corresponding floating diffusion and read out        collectively, and    -   a partial additive readout mode in which, for each of the pixels        of the given unit, less than all of the plurality of electrodes        of the charge holding element of the respective pixel are turned        on while the charge holding element of the respective pixel        receives the electric charge from the photoelectric conversion        element of the respective pixel and the electric charge of the        charge holding element of each pixel of the given unit is added        together by the corresponding floating diffusion and read out        collectively.

(28) The imaging device of any one of (21) through (37), furthercomprising:

a control circuit that controls operations of the plurality of pixels,

wherein the control circuit is configured to cause a given pixel of theplurality of pixels to perform a partial readout operation that includesturning on less than all of the plurality of electrodes of the chargeholding element of the given pixel while the charge holding element ofthe given pixel receives the electric charge from the photoelectricconversion element of the given pixel.

(29) The imaging device of any one of (21) through (37),

wherein each of the plurality of pixel includes a first transfer gatethat selectively electrically separates the photoelectric conversionelement of the respective pixel from the charge holding element of therespective pixel, and a second transfer gate that selectivelyelectrically separates the charge holding element of the respectivepixel from the corresponding floating diffusion.

(30) The imaging device of any one of (21) through (37),

wherein, for each of the plurality of pixels:

-   -   the charge holding element includes a plurality of sub-regions        each corresponding to one of the plurality of electrodes, and    -   the plurality of sub-regions are arranged in series between the        first and second transfer gates.

(31) The imaging device of any one of (21) through (37),

wherein, for each of the plurality of pixels:

-   -   the charge holding element includes a plurality of sub-regions        each corresponding to one of the plurality of electrodes, and    -   the plurality of sub-regions are arranged such that each adjoins        the photoelectric conversion element of the respective pixel        with no other one of the plurality of sub-regions intervening        therebetween.

(32) The imaging device of any one of (21) through (37),

wherein, for each of the plurality of pixels, the plurality ofsub-regions are arranged such that a first direction is transverse to asecond direction,

the first direction is a direction in which charge is transferred intothe charge holding element through the first transfer gate, and

the second direction is a direction in which charge is transferred outfrom the charge holding element through the second transfer gate.

(33) The imaging device of any one of (21) through (37),

wherein, for each of the plurality of pixels:

-   -   the charge holding element includes a plurality of sub-regions        each corresponding to one of the plurality of electrodes,    -   the plurality of sub-regions are arranged such that a first        direction is transverse to a second direction,    -   the first direction is a direction in which charge is        transferred into the charge holding element, and    -   the second direction is a direction in which charge is        transferred out from the charge holding element.

(34) The imaging device of any one of (21) through (37),

wherein the charge holding element of each of the plurality of pixels isconfigured such that at least one of the plurality of electrodes thereofalso controls transfer of the electric charge from the photoelectricconversion element of the respective pixel to the charge holding elementof the respective pixel.

(35) The imaging device of any one of (21) through (37),

wherein, for a given pixel of the plurality of pixels, at least one ofthe plurality of electrodes of the charge holding element thereof is adifferent size from at least one other of the plurality of electrodes ofthe charge holding element thereof.

(36) The imaging device of any one of (21) through (37),

wherein each of the plurality of pixels further includes aphotoelectric-conversion-element-reset gate that abuts the photoelectricconversion element and selectively connects the photoelectric conversionelement to a reset drain.

(37) The imaging device of any one of (21) through (36),

wherein each of the plurality of pixels further includes a lightshielding unit configured to shield the charge holding element from theincident light, and an electrode of at least one of the holding units isdirectly electrically connected to the light shielding unit.

(38) A method of driving an imaging device that includes a plurality ofpixels that each include a photoelectric conversion element thatconverts incident light into an electric charge and a charge holdingelement that receives the electric charge from the photoelectricconversion element, temporarily holds the electric charge, and transfersthe electric charge to a corresponding floating diffusion, where foreach of the plurality of pixels, the charge holding element includes aplurality of electrodes, the method comprising:

causing the charge holding element of a given pixel of the plurality ofpixels to transfer the electric charge held therein to the correspondingfloating diffusion by sequentially turning off the plurality ofelectrodes of the charge holding element of the given pixel.

(39) The method of (38), further comprising:

turning on less than all of the plurality of electrodes of the givenpixel while the electric charge is received from the photoelectricconversion element by the charge holding element.

(40) An electronic apparatus comprising an imaging device that includesa plurality of pixels in a two-dimensional array, each including:

a photoelectric conversion element that converts incident light into anelectric charge; and

a charge holding element that receives the electric charge from thephotoelectric conversion element, and transfers the electric charge to acorresponding floating diffusion,

wherein, for each of the plurality of pixels, the charge holding elementincludes a plurality of electrodes.

(41) An electronic apparatus comprising the imaging device of any one of(21) through (37).

What is claimed is:
 1. An imaging device, comprising: a plurality ofpixels in a two-dimensional array, each including: a photoelectricconversion element that converts incident light into electric charge;and a charge holding element that receives the electric charge from thephotoelectric conversion element, and transfers the electric charge to acorresponding floating diffusion, wherein, for each of the plurality ofpixels, the charge holding element includes a plurality of electrodes.2. The imaging device of claim 1, further comprising: a control circuitthat controls operations of the plurality of pixels, wherein the controlcircuit is configured to cause the charge holding element of a givenpixel of the plurality of pixels to transfer the electric charge heldtherein to the corresponding floating diffusion by sequentiallysupplying an OFF potential to the plurality of electrodes of the givenpixel.
 3. The imaging device of claim 1, further comprising: a controlcircuit that controls operations of the plurality of pixels, wherein thecontrol circuit is configured to drive the plurality of pixels toperform a global shutter imaging operation.
 4. The imaging device ofclaim 1, wherein the plurality of pixels are grouped into units eachcomprising j pixels, j being an integer greater than 1, where each ofthe pixels that is included in a same unit corresponds to a samefloating diffusion.
 5. The imaging device of claim 4, furthercomprising: a control circuit that controls operations of the pluralityof pixels, wherein the control circuit is configured to cause a givenunit to perform an additive readout operation that includes transferringthe electric charges held in the respective charge holding elements ofeach of the pixels of the given unit to the corresponding floatingdiffusion such that the corresponding floating diffusion adds togetherthe electric charges transferred from the pixels of the given unit. 6.The imaging device of claim 4, further comprising: a control circuitthat controls operations of the plurality of pixels, wherein the controlcircuit is configured to cause a given unit to perform a partialadditive readout operation including: for each of the pixels of thegiven unit, turning on less than all of the plurality of electrodes ofthe charge holding element of the respective pixel while the chargeholding element of the respective pixel receives the electric chargefrom the photoelectric conversion element of the respective pixel, andtransferring the electric charges held in the respective charge holdingelements of each of the pixels of the given unit to the correspondingfloating diffusion such that the corresponding floating diffusion addstogether the electric charges transferred from the pixels of the givenunit.
 7. The imaging device of claim 4, further comprising: a controlcircuit that controls operations of the plurality of pixels, wherein thecontrol circuit is configured selectively read out a given unitaccording to one of a plurality of readout modes that the controlcircuit is configured to selectively switch between, the plurality ofreadout modes including: an individual pixel readout mode in which theelectric charge of the charge holding element of each pixel of the givenunit is read out individually, an additive readout mode in which theelectric charge of the charge holding element of each pixel of the givenunit is added together by the corresponding floating diffusion and readout collectively, and a partial additive readout mode in which, for eachof the pixels of the given unit, less than all of the plurality ofelectrodes of the charge holding element of the respective pixel areturned on while the charge holding element of the respective pixelreceives the electric charge from the photoelectric conversion elementof the respective pixel and the electric charge of the charge holdingelement of each pixel of the given unit is added together by thecorresponding floating diffusion and read out collectively.
 8. Theimaging device of claim 1, further comprising: a control circuit thatcontrols operations of the plurality of pixels, wherein the controlcircuit is configured to cause a given pixel of the plurality of pixelsto perform a partial readout operation that includes turning on lessthan all of the plurality of electrodes of the charge holding element ofthe given pixel while the charge holding element of the given pixelreceives the electric charge from the photoelectric conversion elementof the given pixel.
 9. The imaging device of claim 1, wherein each ofthe plurality of pixel includes a first transfer gate that selectivelyelectrically separates the photoelectric conversion element of therespective pixel from the charge holding element of the respectivepixel, and a second transfer gate that selectively electricallyseparates the charge holding element of the respective pixel from thecorresponding floating diffusion.
 10. The imaging device of claim 9,wherein, for each of the plurality of pixels: the charge holding elementincludes a plurality of sub-regions each corresponding to one of theplurality of electrodes, and the plurality of sub-regions are arrangedin series between the first and second transfer gates.
 11. The imagingdevice of claim 9, wherein, for each of the plurality of pixels: thecharge holding element includes a plurality of sub-regions eachcorresponding to one of the plurality of electrodes, and the pluralityof sub-regions are arranged such that each adjoins the photoelectricconversion element of the respective pixel with no other one of theplurality of sub-regions intervening therebetween.
 12. The imagingdevice of claim 11, wherein, for each of the plurality of pixels, theplurality of sub-regions are arranged such that a first direction istransverse to a second direction, the first direction is a direction inwhich charge is transferred into the charge holding element through thefirst transfer gate, and the second direction is a direction in whichcharge is transferred out from the charge holding element through thesecond transfer gate.
 13. The imaging device of claim 1, wherein, foreach of the plurality of pixels: the charge holding element includes aplurality of sub-regions each corresponding to one of the plurality ofelectrodes, the plurality of sub-regions are arranged such that a firstdirection is transverse to a second direction, the first direction is adirection in which charge is transferred into the charge holdingelement, and the second direction is a direction in which charge istransferred out from the charge holding element.
 14. The imaging deviceof claim 1, wherein the charge holding element of each of the pluralityof pixels is configured such that at least one of the plurality ofelectrodes thereof also controls transfer of the electric charge fromthe photoelectric conversion element of the respective pixel to thecharge holding element of the respective pixel.
 15. The imaging deviceof claim 1, wherein, for a given pixel of the plurality of pixels, atleast one of the plurality of electrodes of the charge holding elementthereof is a different size from at least one other of the plurality ofelectrodes of the charge holding element thereof.
 16. The imaging deviceof claim 1, wherein each of the plurality of pixels further includes aphotoelectric-conversion-element-reset gate that abuts the photoelectricconversion element and selectively connects the photoelectric conversionelement to a reset drain.
 17. The imaging device of claim 1, whereineach of the plurality of pixels further includes a light shielding unitconfigured to shield the charge holding element from the incident light,and an electrode of at least one of the holding units is directlyelectrically connected to the light shielding unit.
 18. A method ofdriving an imaging device that includes a plurality of pixels that eachinclude a photoelectric conversion element that converts incident lightinto electric charge and a charge holding element that receives theelectric charge from the photoelectric conversion element, temporarilyholds the electric charge, and transfers the electric charge to acorresponding floating diffusion, where for each of the plurality ofpixels, the charge holding element includes a plurality of electrodes,the method comprising: causing the charge holding element of a givenpixel of the plurality of pixels to transfer the electric charge heldtherein to the corresponding floating diffusion by sequentially turningoff the plurality of electrodes of the charge holding element of thegiven pixel.
 19. The method of claim 18, further comprising: turning onless than all of the plurality of electrodes of the given pixel whilethe electric charge is received from the photoelectric conversionelement by the charge holding element.
 20. An electronic apparatuscomprising an imaging device that includes a plurality of pixels in atwo-dimensional array, each including: a photoelectric conversionelement that converts incident light into electric charge; and a chargeholding element that receives the electric charge from the photoelectricconversion element, and transfers the electric charge to a correspondingfloating diffusion, wherein, for each of the plurality of pixels, thecharge holding element includes a plurality of electrodes.